US20120308052A1 - Microphone Assembly - Google Patents
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- US20120308052A1 US20120308052A1 US13/505,599 US201013505599A US2012308052A1 US 20120308052 A1 US20120308052 A1 US 20120308052A1 US 201013505599 A US201013505599 A US 201013505599A US 2012308052 A1 US2012308052 A1 US 2012308052A1
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/181—Low frequency amplifiers, e.g. audio preamplifiers
- H03F3/183—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
- H03F3/187—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only in integrated circuits
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
- H03F3/45928—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection using IC blocks as the active amplifying circuit
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/375—Circuitry to compensate the offset being present in an amplifier
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45101—Control of the DC level being present
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45136—One differential amplifier in IC-block form being shown
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45586—Indexing scheme relating to differential amplifiers the IC comprising offset generating means
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45588—Indexing scheme relating to differential amplifiers the IC comprising offset compensating means
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2410/00—Microphones
Abstract
Description
- Mic or microphone are generic terms used to describe transducers that convert acoustic energy into electrical energy, or more precisely sound waves into electrical signals. There are a number of different types of microphones in common use. These microphones employ different operating principles such as electrostatics, electromagnetism, piezo-electric effect, etc., and accordingly vary in terms of the acoustic characteristics they display. Selection of a microphone for a particular application is based on the acoustic characteristics.
- Microphones providing high-quality reproduction of sound are desirable in a variety of appliances and applications, for example, in communication devices such as cell-phones and consumer electronics such as voice recorders, hearing aids and video cameras. In addition, applications such as Internet telephony and sound recording techniques as used in the film, television and music industry also require microphones that provide distortion-free audio reproduction, regardless of interference of moderate to high amplitude ambient noise.
- High performance microphones and their associated circuitries, together referred to as microphone assemblies, are evolving at a rapid pace to cater to the need for higher-quality audio. This evolution typically involves improving the performance of the microphones while at the same time simplifying their design and fabrication. The advent of Integrated circuit (IC) technology has contributed to the popularity of small-sized consumer appliances, such as cell-phones, and has, thereby, led to the development of more compact microphones assemblies.
- Compact microphone assemblies are smaller and have lesser number of components. However, the reduction in the size or the number of components can adversely affect the acoustic characteristics of a microphone assembly. For example, a large dynamic range or a low electromagnetic interference (EMI) sensitivity may be difficult to achieve in a compact microphone assembly. Thus, the need for reduction in size of microphone assemblies contradicts the demand for high-quality audio.
- The subject matter described herein is directed towards a high-quality, compact microphone interface for use in electronic devices such as cell-phones, telephones, laptops, hearing aids, camcorders and so on. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter.
- The microphone interface described herein enables direct coupling of a microphone with a preamplifier. In one implementation of the present subject matter, the microphone interface includes a DC servo loop. The DC servo loop provides a DC path for supplying a DC bias current to the microphone. Additionally, the DC servo loop includes an AC ground to provide an AC path for the AC output obtained from the microphone. The AC path and the DC path separate the AC output of the microphone from the DC bias current to facilitate further processing of the AC output.
- In one embodiment, the microphone interface is implemented as an integrated circuit, engaging reduced number of pin interfaces and external components.
- The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.
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FIG. 1 illustrates a block diagram of a typical microphone assembly. -
FIG. 2 shows a typical configuration of the microphone assembly for implementation on an integrated circuit (IC). -
FIG. 3 illustrates another typical configuration of a microphone assembly for achieving a reduction in components and IC pins. -
FIG. 4 illustrates a block diagram representation of an exemplary microphone assembly in accordance with an embodiment of the present subject matter. -
FIG. 5 illustrates an exemplary configuration for the implementation of microphone assembly ofFIG. 4 on an IC in accordance with an embodiment of the present subject matter. -
FIG. 6 illustrates an implementation of the microphone interface ofFIG. 4 for incorporating an internal microphone and an external microphone in accordance with one embodiment of the invention. -
FIG. 7 illustrates a digital control module associated with the microphone interface according to one embodiment of the invention. - The disclosed subject matter relates to a microphone assembly for high-quality, low distortion audio reproduction. In particular, the subject matter relates to a configuration of a microphone assembly to provide a reduction in the count of IC (integrated circuit) pins and the number of external components incorporated therein. Such a microphone assembly may be implemented in a variety of electronic devices, for example, cell-phones, hearing aids, audio-video recorders, laptops and so on. The microphone assembly is configured to be interfaced with the signal processing circuits of such electronic devices.
- The microphone assembly of the present subject matter includes a microphone interface that enables a direct coupling or capacitor-less coupling of inputs from a microphone to a preamplifier. The microphone interface further provides for a reduction in the number of external components and eliminates use of large size components that may make a typical microphone interface bulky and difficult to fabricate on an IC.
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FIG. 1 illustrates a block diagram of atypical microphone assembly 100 incorporated in an electronic device. Themicrophone assembly 100 includes an acoustic transducer in the form of amicrophone 102 to capture sound wave(s) and detect the varying sound pressure levels of the captured sound waves. Accordingly, themicrophone assembly 100 generates an electrical output in accordance with the varying sound pressure levels detected by themicrophone 102. Themicrophone 102 is provided with a bias voltage for generating an electrical output. The bias voltage may be provided by apower supply 104 associated with themicrophone 102. - The electrical output generated by the
microphone 102 is a mic level signal, and is generally small and practically unfit for any signal processing purposes. The signal processing of the mic level signal is possible once the mic level signal is amplified, say to a line level signal. The amplification of the mic level signal can be performed by apreamplifier 108 included in themicrophone assembly 100. Also included in the microphone assembly is amicrophone interface 106 that acts as an interface between themicrophone 102 and thepreamplifier 108. In some implementations, thepreamplifier 108 may be in-built within themicrophone interface 106. - In operation, the
microphone interface 106 receives the mic level signal from themicrophone 102 and provides the mic level signal to thepreamplifier 108, which amplifies the mic level signal to the line level signal. It is desired that only the mic level signal from themicrophone 102 be coupled to thepreamplifier 108. For the purpose, themicrophone interface 106 may include filtering components to remove noise signals and also decouple the bias voltage that may contribute as noise when received and amplified by thepreamplifier 108. - After undergoing amplification at the
preamplifier 108, the line level signal is communicated to asignal processing module 110. Thesignal processing module 110 may facilitate the conversion of the output of thepreamplifier 108, i.e., the line level signal from an analog format into a digital format for further utilization in the electronic device such as a laptop or a cellular phone. For example, a digital output from thesignal processing module 110 may be recorded onto a disk drive in a digital recording device or may be further processed for transmission over a communication channel. -
FIG. 2 shows a typical circuit configuration of amicrophone assembly 200 fabricated on an IC. The circuit configuration depicts the various components of themicrophone assembly 200 for an electronic device, such as a laptop or a cellular phone. The electronic device may include aninternal microphone 202 in-built within the electronic device and anexternal microphone 204 that may be plugged into the electronic device. - A pair of hook-switch detectors 206-1 and 206-2 detects the insertion of the
external microphone 204 into the electronic device and indicates the insertion to a microprocessor (not shown in figure) of the electronic device. On detecting the presence of theexternal microphone 204 the microprocessor facilitates the connection of a power source to theexternal microphone 204. - Specifically, the power source provides a bias voltage to the
external microphone 204. The bias voltage is supplied by afirst micbias amplifier 208, which may be implemented, for example, as a voltage buffer. Thefirst micbias amplifier 208 supplies DC power as bias voltage to theexternal microphone 204 though afirst bias resistor 210. Thefirst micbias amplifier 208 and thefirst bias resistor 210 are fabricated on the IC and are connected to afirst filtering capacitor 212 via a firstexternal micbias pin 214. Thefirst filtering capacitor 212 blocks noise components present in the DC power provided by thefirst micbias amplifier 208. - Further, the microprocessor operates an on-
chip switch 216 to provide the bias voltage to theexternal microphone 204 through an externalmic bias resistor 218. On receiving the bias voltage, theexternal microphone 204 is activated for use. In usage, theexternal microphone 204 generates an electrical output, typically in the form of an alternating current (AC) signal. The AC signal results in a corresponding potential difference or AC voltage across the externalmic bias resistor 218. Further, the AC voltage is supplied to an on-chip preamplifier (not shown in the figure) through IC pins 220-1 and 220-2, connected across the externalmic bias resistor 218. - The on-chip preamplifier reads the AC voltage developed across the external
mic bias resistor 218, in the presence of the DC bias voltage supplied by thefirst micbias amplifier 208. Further, the AC voltage generated by theexternal microphone 204 is small, such as in the order of a few millivolts, while on other hand the DC bias voltage is much larger, such as in the order of a few hundred millivolts. To enable the on-chip preamplifier to retrieve and amplify only the AC voltage, a first pair of AC coupling capacitors 222-1 and 222-2 are connected across the externalmic bias resistor 218 to block the bias voltage. - In order to appropriately block the bias voltage, large size AC coupling capacitors 222-1 and 222-2 are required. The typical values of these capacitors is in the range of about 200 nanoFarad to 1 microFarad. The large size of the AC coupling capacitors 222-1 and 222-2 make them unsuitable for incorporation within the IC. In such a case, the AC coupling capacitors 222-1 and 222-2 are implemented as external components, thereby making the
entire microphone assembly 200 bulky. - Similar to the
external microphone 204, theinternal microphone 202 also generates an electrical output in the form of an AC voltage. The AC voltage from theinternal microphone 202 is coupled to the on-chip preamplifier via a second pair of AC coupling capacitors 224-1 and 224-2, connected across an internalmic bias resistor 226 using IC pins 228-1 and 228-2. Similar to the function of the first pair of AC coupling capacitors 222-1 and 222-2, the second pair of AC coupling capacitors 224-1 and 224-2 also decouple the bias voltage supplied to theinternal microphone 202 through asecond micbias amplifier 230. An on-chipsecond bias resistor 232 and asecond filtering capacitor 234 are associated with thesecond micbias amplifier 230 to serve as noise filtering components. In addition, thesecond micbias amplifier 230 and thesecond bias resistor 232 are implemented on the IC and are connected to thesecond filtering capacitor 234 via a secondexternal micbias pin 236. - The above described circuit configuration of the
microphone assembly 200 includes numerous components. A few components are incorporated on the IC while a significant number of components such as the first and the second pair of AC coupling capacitors 222-1 and 222-2 as well as 224-1 and 224-2 are external to the IC and are interfaced with the components on the IC though IC pins. Specifically, themicrophone assembly 200 includes as many as eight external components interfaced to the on-chip components utilizing up to eight IC pins. The external components are depicted to be enclosed within the dottedenclosure 238. Such external components reduce the compactness of themicrophone assembly 200, thus making it bulky. Several approaches have been developed for reducing the number of components used in microphone assemblies and also reducing the number of IC pins -
FIG. 3 illustrates a typical configuration of amicrophone assembly 300 fabricated in an IC for attaining reduction in the number of external components and IC pins. The configuration of themicrophone assembly 300 enables the implementation of both aninternal microphone 302 as well as anexternal microphone 304 in an electronic device. - To activate the
internal microphone 302, a microprocessor (not shown inFIG. 3 ) of the electronic device closes an internal mic path by closing a first pair of switches 306-1 and 306-2 to connect an on-chip voltage source 308 to theinternal microphone 302. The on-chip voltage source 308 supplies a DC bias voltage to theinternal microphone 302 through afirst bias resistor 310 incorporated on the IC and through a firstbias pin interface 312. The DC bias voltage activates theinternal microphone 302 to generate an electrical output. The electrical output from theinternal microphone 302 is provided to a preamplifier 314. The preamplifier 314 can be implemented on the IC in the form of a differential amplifier. - Similarly, when the microprocessor detects the insertion of the
external microphone 304 into the electronic device, the microprocessor enables a second pair of switches 316-1 and 316-2 to close an external mic path to supply the DC bias voltage from the on-chip voltage source 308 to theexternal microphone 304. The DC bias voltage is supplied through asecond bias resistor 318, which may be incorporated within the IC. A secondbias pin interface 320 is used to couple thesecond bias resistor 318 to theexternal microphone 304. - A first mic input pin 322-1 and a second mic input pin 322-2 are engaged to couple the output of the
internal microphone 302 and theexternal microphone 304, respectively, to the preamplifier 314. The electrical output of themicrophones microphones enclosure 326 depicted in the figure, encloses the external components. - The electrical output from the
internal microphone 302 is received at the input terminal of the preamplifier 314 connected to the mic input pin 322-1. Similarly, the output from theexternal microphone 304 is fed to the input terminal of the preamplifier 314 connected to the mic input pin 322-2. In one example, the output from theinternal microphone 302 may be connected to a non-inverting input of the preamplifier 314 and the output from theexternal microphone 304 may be connected to an inverting input of the preamplifier 314. - In a situation where the
internal microphone 302 is operable, the electrical output from theinternal microphone 302 is sensed at the non-inverting input while the inverting input connected to second mic input pin 322-2 senses the DC bias voltage as well as the potential drop that the electrical output from theinternal microphone 302 generates acrossfirst bias resistor 310. Likewise, when theexternal microphone 304 is functional, the preamplifier 314 reads the output of theexternal microphone 304 at its inverting input, while the non-inverting input, connected the first mic input pin 322-2, reads the DC bias voltage along with the potential drop generated across thesecond bias resistor 318 due to theexternal microphone 304. - Thus, as apparent, an audio path for audio frequency signals from the
microphones microphones - Further, the external mic path is abruptly closed or opened at instances when the
external microphone 304 is attached or removed from the electronic device. - This may provide a large DC input to the preamplifier 314. This large DC input may saturate the output of the
microphone assembly 300 and/or may often result in an undesirable high-amplitude ‘pop’ sound that may be heard at the output of the electronic device. - As illustrated, the configuration of the
microphone assembly 300 provides reduction of components and IC pins only to a small extent by employing four IC pins and two external components, but escalates problems such as noise and EMI. -
FIG. 4 illustrates a block diagram representation of anexemplary microphone assembly 400 for high-quality audio reproduction, in accordance with an embodiment of the present subject matter. Themicrophone assembly 400 includes amicrophone interface 402 to couple amicrophone 404 with an on-chip preamplifier 406 for providing a distortion-free audio while using reduced number of components. In one embodiment, themicrophone interface 402 incorporates aDC servo loop 408. TheDC servo loop 408 separates the path of the AC output of themicrophone 404 from the path of the DC bias current needed to bias themicrophone 404. This provides for segregation of the path of the microphone AC output, which is incapable of being amplified in the presence of a much larger DC bias current. In addition, theDC servo loop 408 eliminates the use of large size capacitors customarily used as DC blocking capacitors for AC coupling of the output of themicrophone 404 to the on-chip preamplifier 406. Thus in other words, themicrophone interface 402 provides for capacitor-less coupling of themicrophone 404. Themicrophone interface 402 described herein provides for direct coupling or DC coupling of themicrophone 404 to thepreamplifier 406. - The output of the
microphone 404 is a small AC current, which is perceived at the input of thepreamplifier 406 as a voltage drop with respect to anAC ground 410, when measured across a sensing resistor (not shown in figure). The DC bias current required to be provided to themicrophone 404 is variable and depends on various factors such as the terminal voltages, temperature, and manufacturing conditions. An optimum DC bias current required by themicrophone 404 is sensed and accordingly supplied by theDC servo loop 408 to themicrophone 404. For the purpose, theDC servo loop 408 includes aservo amplifier 412 and a controlledDC source 414. Theservo amplifier 412 determines the bias current requirement of themicrophone 404 and accordingly directs the controlledDC source 414 to alter the DC current supplied to themicrophone 404. Also, theDC servo loop 408 is configured to maintain a DC potential at the input of thepreamplifier 406 such that the DC potential is equal to the DC bias provided to themicrophone 404. - In one embodiment, the
servo amplifier 412 may be associated with aslew boost module 416. Theslew boost module 416 is typically included in theDC servo loop 408 to enhance the response time of theservo amplifier 412. Adigital control module 418 associated with theDC servo loop 408 operates theslew boost 416 at instances when faster response is desired from theservo amplifier 412. In addition, thedigital control module 418 interacts with theDC servo loop 408 to eliminate any DC bias voltage that may get linked from themicrophone interface 402 to the input of thepreamplifier 406. The operation of thedigital control module 418 to activate theslew boost module 416 and to eliminate the DC bias voltage is elaborated later. -
FIG. 5 illustrates anexemplary configuration 500 for the implementation of themicrophone assembly 400 on an IC, in accordance with an embodiment of the present subject matter. Theconfiguration 500 is described in conjunction with the concepts described withFIG. 4 . In one embodiment, themicrophone 404 is connected to theDC servo loop 408, incorporated on the IC, using a firstinterface pin interface 502. The firstinterface pin interface 502 also couples themicrophone 404 to thepreamplifier 406. In one implementation, thepreamplifier 406 is implemented on the IC as a differential amplifier, termed aspreamp opamp 504 hereinafter. The preamp opamp 504 reads the output from themicrophone 404. - The
DC servo loop 408 interfaced with thepreamp opamp 504 senses the signals from themicrophone 404 to thepreamp opamp 504. TheDC servo loop 408, as aforementioned, includes theservo amplifier 412, which may be implemented using an operational amplifier (OPAMP), referred to as aservo opamp 506 hereinafter. The servo opamp 506 senses the signals from themicrophone 404 to determine the biasing requirement of themicrophone 404 and varies the gate voltage of a field effect transistor (FET) 508 to control the bias current provided to themicrophone 404 from a DCbias voltage supply 509. TheFET 508 is interfaced with abandwidth limiting capacitor 510 via asecond pin interface 512. In one implementation, theFET 508 and thebandwidth limiting capacitor 510 are included within the controlledDC source 414. - The
bandwidth limiting capacitor 510 causes theDC servo loop 408 to provide high impedance to the AC signals from themicrophone 404. It should be noted that the frequency of the AC signals from themicrophone 404 corresponds to the frequency of audio signals. Hence, AC signals whose frequency corresponds to the frequency of audio signals are restricted from entering theDC servo loop 408, while low frequency signals, mainly associated with the large DC bias current, enter the servo loop and are prevented from being received and amplified by thepreamp opamp 504. For example, thebandwidth limiting capacitor 510 may have a capacitance of the order of one microFarad and thus, signals having a frequency below 50 Hz may be disallowed from being amplified. - To eliminate any other noise that may originate from within a component of the
microphone interface 402, all connections made between the components and thepreamplifier 406 are made to provide a differential signal. For example, theservo amplifier 412 is connected to provide a differential input to thepreamp opamp 504 to facilitate rejection of the associated noise. Also, anon-inverting opamp 514 with a feedback loop implemented as theAC ground 410 is connected differentially across thepreamp opamp 504. Thenon-inverting opamp 514 is connected to one end of thepreamplifier 406 through amic bias resistor 516. In order to make the input differential at the other end of thepreamp opamp 504, thenon-inverting opamp 514 is connected to the other end via adifferential resistor 518. Themic bias resistor 516 and thedifferential resistor 518 have the same resistance. In one example, the resistance is about two kilo-ohms. - The
microphone interface 402 provides for cancellation of noise for providing a noise-free audio while at the same time engages less number of components thereby becoming compact. In one implementation, themicrophone interface 402, as explained above, is implemented using two IC pin interfaces and one external component. In another implementation, themicrophone interface 402 is implemented using three IC pin interfaces and one external component to include an internal microphone as well as an external microphone, as explained below. -
FIG. 6 illustrates animplementation 600 of themicrophone interface 402 for incorporating aninternal microphone 602 and anexternal microphone 604 in accordance with one embodiment of the invention. Theimplementation 600 is described in conjunction with the terms and concepts described inFIGS. 4-5 . In the present embodiment, themicrophone interface 402 includes amicrophone switch 605 implemented to enable switching between theinternal microphone 602 and theexternal microphone 604. - The
microphone switch 605 is coupled to an internal mic switch 606-1 and an external mic switch 606-2, which are used to connect theinternal microphone 602 and theexternal microphone 604, respectively, to themicrophone interface 402. An internal mic pin interface 608-1 engages theinternal microphone 602 to the internal mic switch 606-1 and an external mic pin interface 608-2 engages theexternal microphone 604 to the external mic switch 606-2. At instances when theexternal microphone 604 is inserted or removed from the electronic device, the microprocessor (not shown in Fig.) of the electronic device enables themicrophone switch 605 to operate the internal mic switch 606-1 or the external mic switch 606-2 to allow activation of either theinternal microphone 602 or theexternal microphone 604. - Typically, pin interfaces of an IC, such as mic pin interfaces 606-1 and 606-2, are metallic and may act as minute antennas to which external EMI may get coupled. The external EMI captured by the mic pin interfaces 606-1 and 606-2 is often converted into a DC signal. This DC signal may get coupled to the
preamp opamp 504 and distort the output from theinternal microphone 602 or theexternal microphone 604. To prevent such distortions due to EMI, it is required that the EMI gets cancelled, and thus restricted from getting amplified by thepreamp opamp 504. - In one embodiment, an
EMI receptor 614 is implemented on the IC. TheEMI receptor 614 captures EMI signals as captured by the mic pin interfaces 606-1 and 606-2. TheEMI receptor 614 is interfaced with thepreamp opamp 504 in such a manner that an EMI input from theEMI receptor 614 is perceived as a differential signal with respect to the EMI signals from the mic pin interfaces 606-1 and 606-2. Consequently, the EMI signals are rejected at the input of thepreamp opamp 504. In one implementation, theEMI receptor 614 is an IC pin interface that is not bounded out of the die pad of the IC. - Also, many a times, mismatches may occur in the small sized components, such as the
servo opamp 506 and thepreamp opamp 504, due to fabrication-related imperfections. Such mismatches typically lead to the generation of an offset voltage, mainly in the form of a DC voltage, at the inputs of theservo opamp 506 and thepreamp opamp 504. The offset voltage may be substantially large and may saturate the output of thepreamp opamp 504. Also, the offset voltage may reduce the useful dynamic range of themicrophone interface 402. - Further, abrupt voltage changes may occur at the output of the
preamp opamp 504 when a gain change is applied at thepreamp opamp 504. For example, a gain change may occur when theexternal microphone 604 is plugged in. This abrupt change in the voltage is, in effect, an abrupt change in the DC level at the output of thepreamp opamp 504, often heard as a ‘pop’ sound. - The offset voltage and the ‘pop’ noise are undesired and are thus required to be eliminated. In one implementation, the
digital control module 418 operably coupled to themicrophone interface 402 is employed to eliminate the offset voltage and the ‘pop’ noise. -
FIG. 7 illustrates animplementation 700 of themicrophone interface 402 incorporating thedigital control module 418 for elimination of the offset voltage and the ‘pop’ noise, in accordance with one embodiment of the invention. Theimplementation 700 is described in conjunction with the terms and concepts introduced inFIGS. 4-6 . - While switching between the
internal microphone 602 and theexternal microphone 604, thepreamp opamp 504 observes a sudden change in its differential input. For example, when theexternal microphone 604 is inserted into the electronic device, there may be a momentary decrease in voltage causing a voltage drop at the inverting input of thepreamp opamp 504 as compared to its non-inverting input. This voltage drop gets amplified by the gain of thepreamp opamp 504 and can saturate the output of thepreamp opamp 504. It should be noted that this voltage drop gets coupled to thepreamp opamp 504 because theDC servo loop 408 may require some response time before the voltage at the non-inverting input may be altered in proportion to the voltage drop that occurred at the inverting input. - In one embodiment, the response time of the
DC servo loop 408 is about 600 milliseconds. The response time of theDC servo loop 408 is mainly due to the DC settling time required by theservo opamp 506. To expedite the DC settling time, theslew boost module 416 is operated by thedigital control module 418 every time a switching occurs. In one example, theslew boost module 416 may be operated at instances when themicrophone switch 605 indicates to thedigital control module 418 the insertion or removal of theexternal microphone 604. When switching occurs, thedigital control module 418 activates theslew boost amplifier 702 and interrupts theservo opamp 506. - In one embodiment, the
slew boost module 416 is implemented using aslew boost amplifier 702 having a DC settling time of about 20 milliseconds. In one embodiment, during the time period when theslew boost amplifier 702 is operational, thedigital control module 418 blocks the output of thepreamp opamp 504 from getting further processed. The time duration is in the order of 20 millisecond and is not perceivable at the output of thepreamp opamp 504. Blocking of the output of thepreamp opamp 504 prevents the ‘pop’ noise and restricts saturation of any further audio stages at the output of thepreamp opamp 504. - The
digital control module 418 has an in-built counter mechanism to govern the operation of theslew boost module 416. The counter mechanism determines a time duration of operation of theslew boost amplifier 702. In one example, the time duration of operation of theslew boost amplifier 702 is about 20 milliseconds. The counter mechanism sends pulses for activation and deactivation of theslew boost amplifier 702, thereby facilitating operation of theslew boost amplifier 702 for the pre-determined time period. - To eliminate the offset voltage, in one implementation, the
digital control module 418 includes a DC calibration unit in-built within thedigital control module 418. The DC calibration unit performs offset calibration to remove a DC offset voltage at the output of themicrophone interface circuit 402. When theinternal microphone 602 and theexternal microphone 604 are idle, for instance when theinternal microphone 602 and theexternal microphone 604 are not operating or are decoupled from themicrophone interface 402, thedigital control module 418 automatically senses and calculates a value of the offset voltage present at the output of themicrophone interface 402. As explained earlier, the offset voltage is mainly a DC offset voltage occurring due to mismatch of the small sized components such as theservo opamp 506 and thepreamp opamp 504 of themicrophone interface circuit 402. In one example, theinternal microphone 602 and theexternal microphone 604 may be decoupled using the internal mic switch 606-1 and external mic switch 606-2, respectively. In another example, internal switches may be provided in series with themicrophones internal microphone 602 may be used to decouple theinternal microphone 602 while a similar switch in series with theexternal microphone 604 may decouple theexternal microphone 604. - The
digital control module 418 sends digital signals to theservo opamp 506 such that these digital signals correspond to the sensed offset voltage. The sending of the digital signals by thedigital control module 418 to theservo opamp 506 corresponds to an operation of sending a DC offset signal with reversed polarity to themicrophone interface 402. In effect, the operation of sending the digital signals to theservo opamp 506 is performed by thedigital control module 418 so as to cancel or nullify the DC offset signal present at the output of themicrophone interface 402. - The sequence of operations performed by the
digital control module 418 may be summarized using an example of a cellular phone. The electronic device is referred to as a cellular phone for the purpose of illustration. The examples, in no way, should be construed to be limiting. It will be appreciated that the following description extends to any electronic device having a microphone assembly. Consider an example where a user of the cellular phone initiates a call. A call initiation request is received by thedigital control module 418, which, in turn, initiates an interface preparation process for the audio circuitry of the cellular phone. The audio circuitry comprises a microphone assembly such as themicrophone assembly 400 that includes themicrophone interface 402. It will be appreciated that the interface preparation process may also be initiated in the electronic device at instances such as while plugging in of the external microphone or switching between the internal and the external microphones. The interface preparation process is herein explained with reference to themicrophone interface 402 and components thereof. - The interface preparation process begins with determining the biasing requirement of the active microphone. As apparent, the active microphone may be the
internal microphone 602 or theexternal microphone 604 depending on the inputs of themicrophone switch 605 provided to thedigital control module 418. As aforementioned, theservo opamp 506 determines the biasing requirement of the active microphone. Once theservo opamp 506 has sensed the biasing requirement of the active microphone, thedigital control module 418 interrupts theservo opamp 506 and activates theslew boost module 416. As mentioned before, theslew boost module 416 is operated to enhance the response time of theservo opamp 506. For this purpose, theslew boost amplifier 702 is operated in parallel to theservo opamp 506. - The
digital control module 418 operates theslew boost module 416 for the time period predetermined by the in-built counter mechanism, and thereafter reactivates theservo opamp 506. On activation, theservo opamp 506 causes the controlledDC source 414 to provide the required bias to the microphone as determined earlier. Thereafter, the microphone is decoupled and the DC calibration unit of thedigital control module 418 senses the amount of the offset voltage present in the input received by thepreamp opamp 504 and provides corresponding digital signals to theservo opamp 506 to nullify the same. The microphone is then connected and the calibratedmicrophone interface 402 is used for normal operation. During normal operation, the path of the AC signal generated by the microphone gets separated from the path of the DC bias signal due to implementation of theDC servo loop 408 as discussed earlier. Further, as all noise signal paths are made differential, the noise signals get effectively rejected at thedifferential preamplifier 406. - Thus, the operation of the
microphone assembly 400 and the associateddigital control module 418 results in generation of high-quality audio reproduction. Themicrophone interface 402 of themicrophone assembly 400 couples amicrophone 404 with thepreamplifier 406 for providing a distortion-free audio while at the same time using reduced number of components. - Although embodiments for microphone assembly and the microphone interface have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as exemplary implementations for the microphone assembly and the microphone interface .
Claims (21)
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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EP09306053 | 2009-11-03 | ||
EP09306053 | 2009-11-03 | ||
EP09306053.1 | 2009-11-03 | ||
PCT/EP2010/065816 WO2011054671A1 (en) | 2009-11-03 | 2010-10-20 | Microphone assembly |
Publications (2)
Publication Number | Publication Date |
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US20120308052A1 true US20120308052A1 (en) | 2012-12-06 |
US9392361B2 US9392361B2 (en) | 2016-07-12 |
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Application Number | Title | Priority Date | Filing Date |
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US13/505,599 Active 2033-08-10 US9392361B2 (en) | 2009-11-03 | 2010-10-20 | Microphone assembly |
Country Status (4)
Country | Link |
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US (1) | US9392361B2 (en) |
EP (1) | EP2330831A1 (en) |
CN (1) | CN102860042B (en) |
WO (1) | WO2011054671A1 (en) |
Cited By (2)
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US20150185867A1 (en) * | 2013-12-30 | 2015-07-02 | Hong Fu Jin Precision Industry (Wuhan) Co., Ltd. | Keyboard assembly and voice-recognition method |
US10412477B2 (en) | 2016-09-19 | 2019-09-10 | Wade Goeke | High fidelity, professional grade microphone system for direct coupling to recording components |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US8897459B2 (en) * | 2012-09-12 | 2014-11-25 | Bose Corporation | Two-way audio communication system with reduced ground noise |
CN103096231A (en) * | 2013-02-16 | 2013-05-08 | 吴建堂 | High loudness electronic hearing aid |
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- 2010-06-10 EP EP10165571A patent/EP2330831A1/en not_active Withdrawn
- 2010-10-20 US US13/505,599 patent/US9392361B2/en active Active
- 2010-10-20 CN CN201080060345.6A patent/CN102860042B/en active Active
- 2010-10-20 WO PCT/EP2010/065816 patent/WO2011054671A1/en active Application Filing
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US6266424B1 (en) * | 1996-11-13 | 2001-07-24 | Vxi Corporation | Electret microphone circuit with low battery disable |
US20080002841A1 (en) * | 2003-07-17 | 2008-01-03 | Baker Michael W | Low-power high-PSRR current-mode microphone pre-amplifier system and method |
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US20150185867A1 (en) * | 2013-12-30 | 2015-07-02 | Hong Fu Jin Precision Industry (Wuhan) Co., Ltd. | Keyboard assembly and voice-recognition method |
US10412477B2 (en) | 2016-09-19 | 2019-09-10 | Wade Goeke | High fidelity, professional grade microphone system for direct coupling to recording components |
Also Published As
Publication number | Publication date |
---|---|
EP2330831A1 (en) | 2011-06-08 |
US9392361B2 (en) | 2016-07-12 |
CN102860042B (en) | 2015-04-29 |
WO2011054671A1 (en) | 2011-05-12 |
CN102860042A (en) | 2013-01-02 |
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